Wheat Tiller -1 (WT-1), a GRAS domain encoding gene, controls both tillering and spikelet number per spike in wheat

Tiller and spikelet numbers are important agronomic traits affecting wheat grain yield, but the molecular mechanisms controlling these traits are largely unknown. We have identified a gene (Wheat Tiller-1, WT-1) that regulates numbers of these two very important agronomic traits. While trying to understand the early events of tiller development in wheat, cross section analysis of the crown region showed that differentiation of the tiller buds and apical meristem into spikelets occurs during early seedling stages. The gene was identified by VIGS silencing using sequence around the VHIID motif of the LS gene of tomato that controls branching. VIGS gene silencing, first using the tomato sequence and then from the gene identified from wheat resulted in uniculm and reduce tiller number phenotype. Overall, the WT-1 showed only 37.6% predicted protein similarity to the LS gene although the VHIID motif was conserved. The gene has three structural copies one each on the three wheat homoeologous group 7 chromosomes. Although share > 98% sequence similarity, the three gene copies showed different expression pattern in various tissues and growth stages. Silencing of the gene via stable RNAi showed reduction in both tiller and spikelet number. SEM analysis of the RNAi plants showed that silencing of WT-1 reduced the tiller bud initiation. Among the progeny of independent RNAi events, variation in both spikelet and tiller numbers correlated with the level of reduction in the gene expression, showing role of the gene in controlling tiller number and spikelet number per spike.